Originally Posted by
joejack951
John, please look into the forces necessary for a body to rotate. Either you are ignoring me or you just don't seem to get it that in order to accelerate a body towards the ground, whether in an arc or even just straight down, there needs to be a force pulling it down. A bike that has simply stopped moving horizontally cannot possibly provide this force. Sure, the bike can stop and the rider can appear to get thrown forward by the bike but that is not what is actually occuring. The cyclist's momentum is carrying them forward and gravity is pushing them down towards the ground. Draw a free body diagram. If you can't point to a force other than gravity (or the bike's weight) pulling down on the rider, you aren't going to appreciably accelerate a human towards the ground.
Joejack,
I am not ignoring you; you are ignoring rotational physics. Gravity accelerates a person in free fall. But if there is already a velocity, that is added to the acceleration of gravity. You simply are not starting from a zero velocity state. It's like an Apollo capsule headed for the moon. (I just watched the movie, Moonshot, this week. It's the fortieth anniversary of the landing on the moon--it's important to me as I was on the rescue force for Apollo 13, but it came down in the wrong ocean.) If when they made their burn in earth orbit and got enough velocity to break free from earth's gravity and be accelerated by the moon (which they did), the amount of velocity that they already had in excess of that needed to break free would be added to their acceleration from the Moon's gravity field.
In a like manner, the above graphic from B.Surendranath Reddy shows very well that horizontal velocity is converted into rotational velocity, at a
tangent to the axis of rotation. The vertical component changes, but it is there, and adds to the acceleration of gravity. The only way for this not to happen would be to apply the breaks and come to a complete stop (not the bike, but the rider) before beginning the fall.
The same is true of the moon shot. If they gave only enough energy to make it to the break-even point (where the earth's and the moon's gravity were equal), the spacecraft would appear to stop. If they had just a bit more velocity, then it would slow down almost to a stop (like the gymnist you alluded to), but then be accelerated toward the moon. But if there were still sufficient energy more than what was necessary to simply get to that point, that would be added to the acceleration of the moon's gravity on the Apollo spacecraft.
The same thing happens to the bicyclist, as is shown by the diagrams from Reddy's website above.
John